Intruder detection system

ABSTRACT

An intruder detection system in which a transmitter transmits a frequency modulated and amplitude modulated signal to a remote receiver in response to a transducer, such as a geophone detector, picking-up seismic impulse created by one or more intruders. In this manner, an operator listening to the receiver can identify the number of intruders, and also can identify the movements of the intruder or intruders, such as walking, running and the like.

United States Patent 11 -1 Lee 1 1 March 6, 1973 [5 1 INTRUDER DETECTIONSYSTEM [56] References Cited [75] Inventor: Robert D. Lee, San Mateo,Calif. UNITED STATES PATENTS [73] Assignee: The United States of Americaas W by f 31323122 211322 iflififiiffiiiij"""""31135233 Zi the 15 i' andSpace 3,387,296 6/1968 Epstein eta]... ....34o/2o7 x Admlmstramn,wdshmgml" 3,480,942 12 1969 Hirschberg ..340/261 [22] Filed: Feb. 12,1971 3,483,562 12/1969 Sante1mann,.lr. ..325/61 X Appl. No.: 115,083

Related US. Application Data Continuation of Ser. No. 768,662, Oct. 18,1966, abandoned. 1

US. Cl. ..325/61, 325/45, 325/113,

340/258 R, 258 A, 258 B, 345 B, 261; 325/45, 61, 139, 113,145

Primary Examiner-Benedict V. Safourek Atto'rneyDarrell G. Brekke and G.T. McCoy [5 7 ABSTRACT An intruder detection system in which atransmitter transmits a frequency modulated and amplitude modulatedsignal to a remote receiver in response to a transducer, such as ageophone detector, picking-up seismic impulse created by one or moreintruders. In this manner, an operator listening to the receiver canidentify the number of intruders, and also can identify the. movementsof the intruder or intruders, such as walking, running and the like.

6 Claims, 4 Drawing Figures ANT- FM 12 1s 16 M 17 av 52 [2| 1 t) t t t Ig 3 AM AM GEOPHONE AMPLIFIER DETECTOR PULSE .F.OSClLLAT( )R mm unsnSWEPT DETECTOR AND AMPLIFIER 20 I AND AuPLnum-z MODULATOR INTEGRATOR 5|.SWEPT CONSTANT 5s VOLTAGE CONTROLLED MULTIVIBRATOR manufactured andused by or for the Government for governmental purposes without thepayment of any royalties therein or therefor.

BACKGROUND OF THE INVENTION The present invention relates to intruderdetection systems, and more particularly to a seismic detecting intruderdetection system.

Various intruder detector systems have been known in which sound orsonic waves are detected through a transducer. Audio frequency signalsare produced in the output of the transducer for operating an alarm oran indicator when the sound detected is above a preselected level oramplitude, or when the frequency thereof is within predeterminedfrequency ranges. Such intruder detector systems are disclosed in thepatent to Lienan et al. US. Pat. No. 2,942,247; Larrick et al. US. Pat.No. 3,049,669; Foster US. Pat. No. 3,379,994; and Bagno US. Pat. No.3,I09,l65.

In the intruder detector systems heretofore employed, the sound of thealarm or indicator was of fixed or constant frequency and did not varywith respect to the movement of the intruder or the number of intruders.Basically, the alarm was either turned on or turned off, and the alarmdid not indicate any factor other than the presence or absence of anintruder.

SUMMARY OF THE INVENTION An intruder detection system in which afrequency modulated and amplitude modulated system is transmitted to aremote receiver in response to a transducer picking-up sound created byone or more intruders and wherein an operator sensing the sound or audiosignal reproduced by the receiver can identify the number of intrudersand the movement of one or more intruders.

It is an object of the present invention to provide an intruderdetection system in which the number of intruders and the movement ofone or more intruders can be identified.

Another object of the present invention is to provide an intruderdetection system in which the sound or audio frequency signal producedin the output of a receiver enables an operator to identify the numberof intruders and the movement of one or more of the intruders.

Another object of the present invention is to provide an intruderdetection system in which a receiver produces an aura] signal for eachseismic impulse, such as a footstep, during the presence of one or moreintruders, which aural signal is an amplitude, frequency varying tone oraudio signal for identifying the number of intruders and the movementofone or more of the intruders. p

Other and further objects and advantages will appear upon perusal of thedetailed description of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of thetelemetering transmitter of the intruder detection system of the presentinvention.

FIG. 2 is a schematic diagram of the telemetering transmitter shown inFIG. I. v 5

FIG. 3 is a block diagram of the receiver employed in the intruderdetection system of the present invention.

FIG. 4 is a schematic diagram of a modification of the telemeteringtransmitter shown in FIGS. 1 and 2 employing an automatic gain controlcircuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Illustrated in FIG. I is thetelemetering transmitter- 10 of the intruder detection system 10 of thepresent invention. EAch detected seismic impulse from one or moreintruders, such as a footstep, produces an aura] signal that changesboth in amplitude and in frequency. The transmitter 10 picks-up eachdetected seismic impulse and transmits an amplitude and frequencymodulated radio frequency signal for each sound to a remote receiver 11(FIG. 3). The remote receiver 11 produces a distinct sweeping audio tonefor each sound pickedup by the transmitter 10. Each tone produced by thereceiver 11 will vary in accordance with the amplitudefrequency thereof.An operator with experience can learn to identify thenumber of intruderspresent and the type of movement in progress by the intruders, such aswalking, running and the like.

The telemetering transmitter 10 comprises a suitable transducer, such asa conventional geophone seismic detector 12, which serves to detect eachseismic impulse produced by one or more intruders, such as a footstep.Each seismic impulse detected will vary both in amplitude and infrequency. In turn, the. geophone detector 12 produces from each seismicimpulse an alternating current signal that varies both in amplitude andin frequency. Such geophone detectors are manufactured by Mark Products,Inc. and Geospace, Inc. with moving magnets. Frequency ranges are in thevicinity of 8-28 cycles and can be up to 200 cycles.

The detector 12 may be located within a building or outside of anyprotective shelter. Within a building, the detector 12 may be placed onthe floor, on the safe, or on a shelf or cabinet for the convenience ofthe area to be monitored. Outside a protective shelter, the detector 12may be buried in the soil, pushed in the soil or placed on top of thesoil. For improved detection, the detector 12 may be vertically orientedon the soil or floor.

A suitable amplifier 15 amplifies the alternating current signal foreach seismic impulse detected by the geophone detector 12. Connected tothe output of the amplifier 15 is a detector and integrator circuit 16,which produces a sawtooth pulse having integrated therein the amplitudeand frequency varying signal produced by the geophone detector 12. Thesawtooth pulse is fed to a suitable pulse amplifier 17.

Connected to the output of the pulse amplifier 17 is a voltagecontrolled multivibrator 20 and a radio frequency oscillator 21. Thus,the output sawtooth signal from the pulse amplifier 17 changes the stateof the voltage controlled multivibrator 20 and frequency wave output ofa complete sweep in the sweep range of 2-3 kHz. Also, the radiofrequency oscillator 21 makes a complete sweep for each sound producedby the geophone detector 12. The output signals produced by themultivibrator 20 and the radio frequency oscillator 21 are fedsimultaneously to a radio frequency amplifier and an amplitude modulatorcircuit 22, which produces for each seismic impulse detected by thegeophone detector 12 a radio frequency signal that is both amplitude andfrequency modulated for transmission through a conventional antenna 23.The magnitude of change in the amplitude modulation of the signal iscontrolled by the'multivibrator 20 and the magnitude of change of thefrequency modulated component is controlled by the sawtooth pulse andthe radio frequency oscillator 21.

A suitable source of power is provided for the transmitter throughconventional batteries 25 and 26. On-off switch 27 is closed foroperating the transmitter 10 by completing the energizing circuit to thebatteries 25 and 26.

The amplifier includes conventional transistorized alternating currentamplifiers 30-32. Through a gain potentiometer 33, the overallamplification of the amplifiers 30-32 is controlled. When a seismicimpulse is detected by the geophone detector 12, such as a footstep ofan intruder, the geophone detector 12 produces an alternating currentsignal varying in amplitude and frequency, which is amplified by theamplifiers 30-32 and fed to the detector and integrator circuit 16.

When the output signal from the amplifier 32 exceeds the forward bias ofa transistor 40 in the detector and integrator circuit 16, thetransistor 40 is turned on or conducts. Forward bias for the transistor40 is derived from a source resistor 41 and a coupling capacitor 42.While the transistor 40 conducts, a capacitor 45 in the detector andintegrator circuit 16 charges. The capacitor 45 discharges at a timeconstant determined by a resistance-capacitance network, which-includesthe capacitor 45 and resistors 46 and 47. The time is equal to C ,,(R R/R R It is the capacitor 45 and the resistors 46 and 47 that form theintegrating network for the detector and integrator circuit 16.

Normally, a transistor 50 of the pulse amplifier 17 is non-conducting.However, the charge stored in the capacitor 45 along with the resistors46 and 47 of the integrating network controls the period of saturationof the transistor 50 and the exponential voltage rise of the sawtoothpulse produced in the output of the pulse amplifier 17. The transistors40 and 50 remain tumed-ofi' or non-conducting until the output signal ofthe amplifier 32 exceeds the forward bias on the transistor 40.

When the pulse amplifier 17 is conducting, or is turned on, the outputsignal therefrom changes the state or mode of the conventionalvoltage-controlled multivibrator 20 over a conductor 51 andsimultaneously frequency modulates the conventional radio frequencyoscillator 21. A radio frequency choke coil 53 is disposed between themultivibrator 20 and the I input signal to the detector and integratorcircuit 16 exradio frequency oscillator 21. For each seismic impulsedetected by the geophone 12, such as a footstep, the multivibrator 20 isswept through a range between 2-3 kHz. It is the exponential portion ofthe output signal from the pulse amplifier 17 that controls the extentof the frequency range for the voltage controlled multivibrator 20. Italso is the exponential portion of the output signal from the pulseamplifier that frequency modulates the radio frequency oscillator 21.Accordingly, for each seismic impulse detected by the geophone detector12, such as a footstep, the radio frequency oscillator 21 is frequencymodulated for a complete sweep while the voltage controlledmultivibrator 20 is swept. While reference is made to the exponentialportion of the pulse for controlling the operation of the radiofrequency oscillator 21 and the multivibrator 20, it is apparent thatthe decay portion of a sawtooth pulse performs the same controloperations.

Connected to the output of the radio frequency oscillator 21 over aconductor 55 and connected to the output of the multivibrator 20 over aconductor 56 is the radio frequency amplifier and amplitude modulatorcircuit 22. It is the output of the multivibrator 20 that amplitudemodulates the radio frequency signal at the input of the radio frequencyamplifier 22 through a connection to the base electrode of a transistor60 in the radio frequency amplifier and modulator circuit 22. Throughthis arrangement, the bias on the transistor 60 is varied or there isbase injection to modulate the radio frequency amplifier and modulatorcircuit 22. The output of the radio frequency oscillator 21 is connectedto the base electrode of the transistor 60 in the radio frequencyamplifier and modulator circuit 22. The collector electrode of thetransistor 60 is coupled to a resonant output circuit 65, which iscoupled to the antenna 23 through a coupling capacitor 61. Forregulating the carrier frequency of the transmitter 10, the inductancesof coils 63 and 64 in the radio frequency oscillator 21 are adjusted tothe same resonant frequen- During standby or quiescent time, only theamplifiers 30-32 and their bias circuits are consuming direct currentpower. The remaining circuits are off. .The re sistance values in theamplifier circuits 30-32 are selected at relative high values to consumevery low standby power from the batteries 25 and 26. Thus, long batterylife is attained by standby operation until the seismic impulse of anintruder is detected by the geophone 12.

In the operation of the transmitter 10, the geophone detector 12 detectseach seismic impulse, such as a footstep, produced by an intruder. Eachseismic impulse has an amplitude and frequency varying tone. Thegeophone detector 12 converts each seismic impulse into an alternatingcurrent signal with amplitude and frequency varying components.

The amplifier 15 amplifies the alternating current signal produced bythe geophone detector and feeds the amplified alternating current signalto the detector and integrator circuit 16. In the exemplary embodiment,the forward bias on the transistor 40 of the detector and integratorcircuit 16 is 0.6 volts. When the ceeds 0.6 volts, which is at a timethe transistor 40 conducts or is turned on. While the transistor 40conducts, the capacitor 45 charges. When the transistor 40 is tumed-off,the capacitor 40 discharges through the resistors 46 and 47. Thedischarge time for the capacitor 40 is between t, and t; and is equal toC R R lR R Thus, the capacitor 45 and the resistors 46 and 47 form asawtooth signal with the amplitude variation and frequency variation ofthe geophone audio frequency signal integrated therein. The time periods1,, hand t are shown in FIG. 1 in connection with the waveformsillustrated therein.

When the transistor 40 of the detector and integrator circuit 16 isturned on, the transistor 50 of the pulse amplifier 17 is turned on,which results in the amplification of the sawtooth pulse. Thus, theexponential rise time t, t of the amplified sawtooth signal is thedischarge time for the capacitor 45 of the resistancecapacitance networkof capacitor 45 and the resistors 46 and 47.

During the exponential rise time of the amplified sawtooth signal, theradio frequency oscillator 21 is turned on to produce a frequencymodulated radio frequency signal having a complete sweep for eachseismic impulse detected by the geophone detector 12. Simultaneously,the voltage controlled multivibrator 20 has its state or mode changedover a frequency range or time period equal to the exponential rise timeof the amplified sawtooth signal, which is equal to a complete sweep foreach sound detected by the geophone detector 12.

The frequency modulated signal in the output of the radio frequencyoscillator 21 is fed to the radio frequency amplifier and amplitudemodulating circuit 22. Simultaneously, the square wave output of themultivibrator 20 is fed to the input of the radio frequency amplifierand amplitude modulating circuit 22 to amplitude modulate the modulatedradio frequency signal. As a result thereof, the antenna 23 transmits anamplitude modulated-frequency modulated radio frequency signal.

ln FIG. 3 is illustrated the receiver 11, which receivers the amplitudemodulated-frequency modulated radio frequency signal from thetransmitter through a suitable antenna 70. This signal is amplified by aconventional radio frequency amplifier 71 and fed to a suitable ratiodetector 72. Ratio detector circuits are commonly employed intransistorized radio receivers, and are capable of detecting bothamplitude modulated radio frequency signals and frequency modulatedradio frequency signals. The ratio detector 72 detects both theamplitude modulated component and the frequency modulated component ofthe radio frequency amplified by the amplifier 71. The output of theratio detector 72 for each seismic impulse, such as a footstep, iscomparable to the amplitude modulating signal input to the radiofrequency amplifier output of the detector and integrator circuit 16.Specifically, the output of the ratio detector for each seismic impulse,such as a footstep, or sweep has two separate components, one theamplitude modulating component and the other the frequency modulatingcomponent.

The output of the ratio dectector 22 is transmitted to an audioamplifier, which feeds the amplified audio cy varying tone representinga seismic impulse from an intrusion.

Illustrated in FIG. 4 is a telemetering transmitter 80, which is amodification of the telemetering transmitter shown in FIG. 1. Items inthe transmitter corresponding to items in the transmitter 10 will beshown with the same reference numeral but accompanies by a prime suffix.

In the telemetering transmitter 10, the amplitude of the amplifiers30-32 of the audio amplifier 15 was controlled manually by the variableresistor 33. In the transmitter 80 an automatic gain control circuit isprovided in lieu of the manually adjusted gain control potentiometer 33.

The telemetering transmitter 80 operates in substantially the samemanner as does the telemetering transmitter 10 in that the geophonedetector 12' senses a seismic impulse, such as a footstep, and producestherefrom an alternating current signal varying in amplitude andfrequency. The transmitter 80 in response to the alternating currentsignal transmits a radio frequency signal which is frequency andamplitude modulated. Toward this end, a radio frequency oscillator isfrequency modulated and a voltage tuned multivibrator changes its stateto amplitude modulate the frequency modulated radio frequency signal.These modulating actions are under the control of a detector andintegrator circuit.

Specifically, in the telemetering transmitter 80, the geophone detector12' senses a seismic impulse, such as a footstep, and feeds to analternating current amplifier an alternating current signal varying inamplitude and in frequency. The alternating current amplifier 85comprises conventional alternating current transistor amplifiers 86-90.Connected to the input circuits of the amplifier 86 is a suitable r-ffilter circuit 91 and connected to the input circuits of the amplifiers87 and 88 are voltage controlled resistors 92 and 93, respectively, inthe form of well-known field-effect transistors. The voltage controlledresistors 92 and 93 form a voltage divider network with resistors 94 and95, respectively.

Connected to the output of the amplifier of the alternating currentamplifier 80 is an automatic gain control detector circuit 100.Associated with the automatic gain control detector circuit is a gaintime constant integrating circuit 101, which comprises capacitors102-104 and resistors 105-106.

The automatic gain control circuit 100 includes a transistor 110, adiode 11 1, and resistors 112 and 113.

The output signal from the'geophone detector 12is r-f filtered by thefilter circuit 91 and amplified by the amplifiers 86-90. The amplifiedalternating current signal is fed to the automatic gain control detectorcircuit 100. When the peak voltage of the amplified altemating currentsignal is above a predetermined magnitude, namely the forward bias onthe transistor 1 10 of the detector circuit 100 established by the diode1 1 1 and the resistors 112 and 1 13, the transistor is turned on orstarts to conduct. This is accomplished through the peaks of the wavesignals appearing in the output of the amplifier 90.

As a consequence thereof, the capacitors 102-104 of the gain timeconstant integrating circuit 101 are charged. The potential across thecapacitors 102-104 will vary the resistance of the voltage controlledresistors 92 and 93 through resistors 115 and 116 and filter capacitors117 and 118. As previously described, the voltage controlled resistors92 and 93 form resistance networks with the resistors 94 and 95,respectively. I g 7 During the quiescent state, or when the geophonedetector 12'does not sense any seismic impulse, such as a footstep,seismic background noises will produce a noise level output in thegeophone detector 12'. Such noise signals will cause the capacitors102-104 to be charged. When the resistance of the voltage controlledresistors 92 and 93 are varied by the noise potential across thecapacitors 102-104, the overall gain of the alternating currentamplifier 85 is decreased until the peak noise signals produced in theoutput of the geophone detector 12'cannot turn on or trigger thetransistor 1 of the automatic gain control circuit 100 by overcoming theforward bias thereof. At this time, the gain is properly adjusted. I

A detector and integrator circuit 16with a transistor 40'is connected tothe output of the amplifier 90, which operates in the manner describedfor the detector and integrator circuit 16. When the output of theamplifier 90 reaches a peak-to-peak quiescent value, any slight increasein the noise level will turn on or trigger the transistor 1 10 of theautomatic gain control detector 100, but it will not turn on or triggerthe transistor 40'of the detector and integrator circuit 16 With anincreasing input signal applied to the amplifier 86 from the geophonedetector l2through the filter 91, the transistor 110 of the automaticgain control detector circuit 100 causes an increase of charge andpotential across the capacitors 102-104 of the gain time constantcircuit 101. This action causes an increase in the gate bias for thevoltage controlled resistors 92 and 93 through the resistors 115 and116, respectively. As a consequence thereof, the resistance between thesource and drain electrodes for the voltage controlled resistors 92 and93 decreases, respectively. Since the voltage controlled resistors arepart of voltage divider networks in conjunction with the resistors 94and 95, respectively, less signal appears across the voltage controlledresistors 92 and 93.

As the charge stored in the capacitors 102-104 of the gain time constantcircuit 101 discharges through the resistors 105 and 106, the resistanceof the voltage controlled resistors 92 and 93 increases and now more.

signal appears across the voltage controlled resistors 92 and 93. Thisaction turns on the transistor 110 of the automatic gain control circuit100 to once again charge the capacitors 102-104 of the gain timeconstant integrating circuit 101.

' Should the capacitors 102-104 of the gain time constant integratingcircuit 101 be fully discharged at the time the transistor 110 of theautomatic gain control circuit 100 is turned on initially, then the gainof the alternating current amplifier 80 is at a maximum. Conversely, ifthe capacitors 102-104 are fully charged at the time the transistor 110is turned on initially, then the gain of the alternating currentamplifier 80 is at a minimum.

The frequency response of the alternating current frequency amplifier 80is limited by the magnitude of the resistors 94. and 95 and the inputinterelectrode capacitance of the voltage controlled resistors 92 and93. In the exemplary embodiment, the frequency range for the alternatingcurrent amplifier is from 5b: to 200hz. This frequency response range isideally suited to the seismic frequency range of the geophone 12 whichhas a peak at 8hz and a maximum of 200hz. It is to be observed that thetransmitter 80, as well as the transmitter 10, operate on the principleof signal impulses and not seismic signature processing. Therefore, theresonance peak characteristics of the geophone detector 12 are employed.The frequency range above referred to in connection with the transmitter80 is equally applicable to the transmitter 10.

During the time the automatic gain control detector is self-adjustingfrom a high maximum gain level, the detector and integrator circuit 16'is turned on to change the state of voltage controlled multivibratorcircuit 20' and to frequency modulate a radio frequency oscillator 21.The output of the voltage controlled multivibrator 20 amplitudemodulates a frequency modulated radio frequency signal fed to a radiofrequency amplifier and modulating circuit 22' by the radio frequencyoscillator 21. This operation is the same as the operation previouslydescribed for the circuits 16, 17, 20, 21 and 22 of transmitter 10.

However, at the time the automatic gain control detector circuit 100approaches the proper gain setting, the transistor 40'of the detectorand integrator circuit 16'tums off, because its the bias resistors 41'and 120 reach the quiescent level, while the automatic gain controldetector circuit 100 is making its final overall gain adjustment.

Should an intruder approach the range of the geophone detector 12, hisfootstep will generate a sound which is amplified by the alternatingcurrent amplifier 80 to turn on the transistor 40' of the detector andintegrator circuit 16'. When intrusion occurs, the gain of thealternating current amplifier 80 also changes. The change is to decreasethe gain. However, the automatic gain control time constant capacitors102-104 and resistors 105 and 106 are set long enough that thealternating current amplifier 15 will recover and be ready in sufficienttime for the next intruder step.

The geophone detector has been employed herein as detecting seismicimpulses. It is apparent that the geophone detector detects seismicvibrations, seismic waves, acoustic waves and the like.

It is to be understood that variations and modifications may be effectedwithout departing from the spirit of the invention and the scope of theappended claims.

What I claim as new and desire to protect by Letters Patent is:

1. Seismic sensor apparatus comprising:

transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto; menas coupled to said transducer means fordetecting the envelope of each of said bursts exceeding a minimumthreshold level and generating a modulating signal which is a functionthereof, said modulating signal comprising a series of pulses; meanscoupled to said detecting means for transmitting an a-m and f-mmodulated r-f signal burst whenever a pulse occurs, said a-m and f-mmodulation each being a function of the particular pulse shape, and saidr-f signal burst duration being substantially the same duration as it'srespective pulse.

2. Seismic sensor apparatus comprising:

transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto;

means coupled to said transducer means for detecting the envelope ofeach of said bursts exceeding a minimum threshold level and generating amodulating signal which is a function thereof, said modulating signalcomprising a series of pulses;

an r-f signal transmitter;

means coupled to said transmitter for modulating said r-f signal inaccordance with said modulating signal;

means for receiving and demodulating said r-f signal;

means coupled to said receiving and demodulating means for generatingsound bursts, a sound burst being generated for and as a result of eachof said pulses, each sound burst having a portion wherein the frequencyis swept.

3. Seismic sensor apparatus comprising:

transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto;

means coupled to said transducer means for generating a modulatingsignal which is a function of th envelopes of said a-c signal burstswhich exceed a predetermined level, said modulating signal comprising aseries of pulses each having an exponential portion, there being onepulse for each burst which exceeds said predetermined level;

an r-f signal transmitter;

means coupled to said transmitter for modulating said r-f signal inaccordance with said modulating signal;

means for receiving and demodulating said r-f signal;

means coupled to said receiving and demodulating means for generatingsound bursts, a sound burst being generated for and a result of each ofsaid pulses, each sound burst having a portion wherein the frequency isswept as a function of the exponential portion of said pulse causingthat sound burst.

4. Seismic sensor apparatus comprising:

transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto;

means coupled to said transducer means for detecting the envelope ofeach of said bursts exceeding'a minimum threshold level and generating amodulating signal which is a function thereof;

a voltage-controlled r-f oscillator capable of generating an r-f signalthe frequency of which is dependent'on the magnitude of an input signal,said voltage-controlled r-f oscillator having an input and an output;

means for coupling said modulating signal to said input of said r-foscillator to frequency modulate said r-f signal in accordance with saidmodulating signal;

a voltage-controlled audio oscillator capable of generating an audiosignal the frequency of which is dependent on the magnitude of an inputsignal, said voltage-controlled audio oscillator having an input and anoutput;

means for coupling said modulating signal to said input of saidvoltage-controlled audio oscillator to I 5. Seismic sensor apparatuscomprising:

transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto;

- means coupled to said transducer means for generating a modulatingsignal which is a function of the envelopes of said a-c signal burstswhich exceed a predetermined level, said modulating signal comprising aseries of pulses, one for each envelope;

a voltage-controlled r-f oscillator capable of generating an r-f signalthe frequency of which is dependent on the magnitude of an input signal,said voltage-controlled r-f oscillator having an input and an putput; 1

means .for coupling said modulating signal to said input of said r-foscillator to frequency modulate said r-f signal in accordance with saidmodulating signal;

a voltage-controlled audio oscillator capable of generating an audiosignal the frequency of which is dependent on the magnitude of an inputsignal, said voltage-controlled audio oscillator having an input and anoutput;

means for coupling said modulating signal to said input of saidvoltage-controlled audio oscillator to frequency modulate said audiosignal in accordance with said modulating signal;

means connected to said output of said audio oscillator for amplifyingand amplitude modulating said frequency-modulated r-f signal generatedby said r-f oscillator, said r-f signal being amplitude modulated inaccordance with said audio signal; and

means connected to said amplifying and modulating means for transmittingsaid frequency and amplitude modulated r-f signal.

6. Transmitter apparatus comprising:

a geophone for generating an a-c signal whenever a seismic impulse isdetected;

means for amplifying, detecting and integrating said a-c signal toproduce a modulating signal; a voltage-controlled r-f oscillatorgenerating an r-f signal and having an input and an output;avoltage-controlled multivibrator generating an output signal and havingan input and output; means for coupling said modulating signal to saidinput of said r-f oscillator to produce an f-m modulated r-f signal atsaid r-f oscillator output; means for coupling said modulating signal tosaid input of said multivibrator to produce an f-m modulated outputsignal; means connected to said output of said r-f oscillator foramplifying and amplitude modulating said modulated r-f signal; saidoutput of said multivibrator being coupled to said amplifying andmodulating means, said modulated r-f signal being amplitude modulated inaccordance with said modulated output signal; and

lated r-f signal.

1. Seismic sensor apparatus comprising: transducer means for sensingseismic impulses and generating a-c signal bursts in response thereto;menas coupled to said transducer means for detecting the envelope ofeach of said bursts exceeding a minimum threshold level and generating amodulating signal which is a function thereof, said modulating signalcomprising a series of pulses; means coupled to said detecting means fortransmitting an a-m and f-m modulated r-f signal burst whenever a pulseoccurs, said a-m and f-m modulation each being a function of theparticular pulse shape, and said r-f signal burst duration beingsubstantially the same duration as it''s respective pulse.
 1. Seismicsensor apparatus comprising: transducer means for sensing seismicimpulses and generating a-c signal bursts in response thereto; menascoupled to said transducer means for detecting the envelope of each ofsaid bursts exceeding a minimum threshold level and generating amodulating signal which is a function thereof, said modulating signalcomprising a series of pulses; means coupled to said detecting means fortransmitting an a-m and f-m modulated r-f signal burst whenever a pulseoccurs, said a-m and f-m modulation each being a function of theparticular pulse shape, and said r-f signal burst duration beingsubstantially the same duration as it''s respective pulse.
 2. Seismicsensor apparatus comprising: transducer means for sensing seismicimpulses and generating a-c signal bursts in response thereto; meanscoupled to said transducer means for detecting the envelope of each ofsaid bursts exceeding a minimum threshold level and generating amodulatiNg signal which is a function thereof, said modulating signalcomprising a series of pulses; an r-f signal transmitter; means coupledto said transmitter for modulating said r-f signal in accordance withsaid modulating signal; means for receiving and demodulating said r-fsignal; means coupled to said receiving and demodulating means forgenerating sound bursts, a sound burst being generated for and as aresult of each of said pulses, each sound burst having a portion whereinthe frequency is swept.
 3. Seismic sensor apparatus comprising:transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto; means coupled to said transducer means forgenerating a modulating signal which is a function of th envelopes ofsaid a-c signal bursts which exceed a predetermined level, saidmodulating signal comprising a series of pulses each having anexponential portion, there being one pulse for each burst which exceedssaid predetermined level; an r-f signal transmitter; means coupled tosaid transmitter for modulating said r-f signal in accordance with saidmodulating signal; means for receiving and demodulating said r-f signal;means coupled to said receiving and demodulating means for generatingsound bursts, a sound burst being generated for and a result of each ofsaid pulses, each sound burst having a portion wherein the frequency isswept as a function of the exponential portion of said pulse causingthat sound burst.
 4. Seismic sensor apparatus comprising: transducermeans for sensing seismic impulses and generating a-c signal bursts inresponse thereto; means coupled to said transducer means for detectingthe envelope of each of said bursts exceeding a minimum threshold leveland generating a modulating signal which is a function thereof; avoltage-controlled r-f oscillator capable of generating an r-f signalthe frequency of which is dependent on the magnitude of an input signal,said voltage-controlled r-f oscillator having an input and an output;means for coupling said modulating signal to said input of said r-foscillator to frequency modulate said r-f signal in accordance with saidmodulating signal; a voltage-controlled audio oscillator capable ofgenerating an audio signal the frequency of which is dependent on themagnitude of an input signal, said voltage-controlled audio oscillatorhaving an input and an output; means for coupling said modulating signalto said input of said voltage-controlled audio oscillator to frequencymodulate said audio signal in accordance with said modulating signal;means connected to said output of said audio oscillator for amplifyingand amplitude modulating said frequency-modulated r-f signal generatedby said r-f oscillator, said r-f signal being amplitude modulated inaccordance with said audio signal; and means connected to saidamplifying and modulating means for transmitting said frequency andamplitude modulated r-f signal.
 5. Seismic sensor apparatus comprising:transducer means for sensing seismic impulses and generating a-c signalbursts in response thereto; means coupled to said transducer means forgenerating a modulating signal which is a function of the envelopes ofsaid a-c signal bursts which exceed a predetermined level, saidmodulating signal comprising a series of pulses, one for each envelope;a voltage-controlled r-f oscillator capable of generating an r-f signalthe frequency of which is dependent on the magnitude of an input signal,said voltage-controlled r-f oscillator having an input and an putput;means for coupling said modulating signal to said input of said r-foscillator to frequency modulate said r-f signal in accordance with saidmodulating signal; a voltage-controlled audio oscillator capable ofgenerating an audio signal the frequency of which is dependent on themagnitude of an input signal, said voltage-controlled audio oscillatorhaving an input and aN output; means for coupling said modulating signalto said input of said voltage-controlled audio oscillator to frequencymodulate said audio signal in accordance with said modulating signal;means connected to said output of said audio oscillator for amplifyingand amplitude modulating said frequency-modulated r-f signal generatedby said r-f oscillator, said r-f signal being amplitude modulated inaccordance with said audio signal; and means connected to saidamplifying and modulating means for transmitting said frequency andamplitude modulated r-f signal.